A pulse-width modulation (PWM) converter which is an example of a conventional power converting apparatus configured with semiconductor devices having self-extinguishing (or self-turn-off) capability like gate turn-off thyristors (GTOs) can perform switching operation regardless of the polarity of a source voltage and the polarity and magnitude of electric current, so that the PWM converter can be controlled to operate at a power factor of 1 in power running mode and at a power factor of −1 in regenerative running mode (refer to Non-patent Document 1, for example).
Non-patent Document 1: “State-of-the-art Electric Railway Engineering” (Investigation Committee on Electric Railway of the Institute of Electrical Engineers of Japan, published Sep. 11, 2000 by Corona Publishing Co., Ltd.) pp 60-67.